Electric hand tool with overload coupling



Aug. 27, 1968 R. HAHNER 3,398,611

ELECTRIC HAND TOOL WITH OVERLOAD COUPLING Filed July 6, 1966 FIG. 1

INVENTOR Reinhard Ha her United States Patent ice 3,398,611 ELECTRIC HAND TOOL WITH OVERLOAD COUPLING Reinhard Hahner, Stuttgart, Germany, assignor to Robert Bosch G.m.b.H., StuttgartfGermany Filed July 6, 1966, Ser. No. 563,272

Claims priority, application G9ermany, July 8, 1965,

10 Claims. (51. s1 52.4

The present invention relates to a hand tool with over load coupling, and more particularly to an electric hand tool with built-in drive motor and coupling means which include an overload coupling and a drive coupling.

It is known to provide electric hand tools of this type with a coupling which, when an adjustable maximum load torque is exceeded, is disengaged. In known constructions of this type, it has been proposed to eliminate the rattlin noise produced by the continuous sliding of the disengaged overload coupling, however, very complicated constructions have resulted, and very great forces have to be taken up by the casing, requiring heavy casings or casings made of expensive materials.

It is one object of the invention to overcome the disadvantages of known electric hand tools with overload couplings, and to provide an electric hand tool in which no substantial forces are transmitted to the casing, so that the same can be made of a light metal or of a plastic material.

Another object of the invention is to provide an electric hand tool in which the forces of an overload spring controlling the overload coupling are taken up only by rotating parts.

Another object of the invention is to provide an electric hand tool in which not the force of the overload sprin of the overload coupling, but the force of another normally much weaker spring has to be overcome for moving the drive coupling to an engaged position in which the tool is rotated.

Another object of the invention is to provide an electric screw driver which, upon axial pressure'against a screw head, assumes an operative position in which a tool holder is coupled to drive means, and which, when further rotation of the tool is blocked by the screw, effects first disengagement of an overload coupling, and then disengagement of the drive coupling.

With these objects in view, one embodiment of the invention comprises a casing adapted to be manually held; a tool holder and a drive means, such as a motor driven drive gear, mounted in the casing for rotation and axial movement; coupling means connecting the tool, holder with the drive means and including an overload coupling, a drive coupling, and a rotary and axially movable coupling member connected with the couplings; an overload spring connecting ,the coupling member with the tool holder and urging the coupling member to a normal position in which the overload coupling is engaged; and a second spring for urging said tool holder and coupling member in said normal position to an inoperative position in which the drive coupling is disengaged. The arrangement is such that the tool holder, the overload coupling, and the coupling member in the normal position, are moved by outer axial pressure produced by a workpiece to a working position in which the drive 3,398,611 Patented Aug. 27, 1968 couplingand the drive means in axial directionso that the drive'means rotates the coupling member idly until the overload spring returns the coupling member to the normal position in which the drive coupling is disengaged and the tool holder with the tool no longer driven.

In the preferred embodiment of the invention, the axially displaced drive means, for example a drive gear, is temporarily locked so that it cannot follow the coupling member returning to the normal position. Releasing means are provided for releasing the locking means and the drive gear when after the coupling member the tool holder has arrived in the normal position so that the initial position of all parts of the tool is restored.

In the preferred embodiment of the invention, the coupling member is a coupling sleeve enveloping a portion of the tool holder and the overload spring, and carrying coupling parts of the overload coupling and of the drive coupling cooperating with other coupling parts on the tool holder and on the drive gear, respectively. An electric hand tool according to the invention obtains a perfect operation, while slide keys, splined shafts, and other complicated parts necessary in prior art constructions, are avoided.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a fragmentary axial sectional view illustratin a hand tool according to the invention as embodied in an electrically operated screw driver;

FIG. 2 is a fragmentary sectional view of a detail of the embodiment of FIG. 1 illustrating the drive coupling in the engaged position;

FIG. 2a is a fragmentary sectional view taken on line Ilia-Ila in FIG. 2;

FIG. 3 is a fragmentary sectional view of the drive coupling in a disengaged and locked position; and

FIG. 3a is a fragmentary sectional view taken on line IIIa-IIIa in FIG. 3.

Referring now to the drawing, a motor shaft 1 of a motor, not shown, mounted in a casing 20, drives over a pair of gears a shaft 2 carrying a pinion 2a meshing with a drive gear 3 which is mounted on a shaft 9 for axial movement. A spring 6 acts on drive gear 3 to move the same to the left as viewed in FIG. 1 into abutment with a spring washer 10 secured in an annular groove of shaft 9. Spring '6 abuts a disk 7 which is also secured to support shaft 9 by a spring washer 8. Drive gear 3 rotates with shaft 9 which is mounted at one end in a ball bearing 11, and at the other end in a recess of a 'tool holder 13. A spring 17 is mounted in the same recess of tool holder 13 and abuts a ball 18 located at the bottom of the recess, and a control member 16' which is guided in a corresponding recess of shaft 9 for axial movement, and has a conical face cooperating with a plurality of locking balls 15 respectively located in bores or recesses extending radially through the wall of sup? port shaft 9. Drive gear 3 has an annular recess 5 having a slanted wall and adapted to receive balls in the position shown in- FIG. 3 if drive gear 3 is moved to the right as viewed in FIG. 3 against the action of spring 6. When in such axially displaced position, the annular groove 5 registers with the bores 14, the conical face of control member 16 urges the balls 15 outward under the action of spring 17 and into the annular groove or recess 5, so that drive gear 3 is locked in the axially displaced position shown in FIG. 3 as long as the force of spring 17 is suflicient to hold locking balls 15 in the locking position shown in FIG. 3. When this force of spring 17 is reduced in a manner which will be explained hereinafter, the force of spring 6 is sufficient to move drive gear 3 to the left from the position shown in FIG. 3 to the position shown in FIG. 1 while the slanted bottom of annular groove 5 urges locking balls 15 inward into bores 14 until the position of FIG. 1 is reached.

As explained above, the rear end of tool holder 13 is mounted on a portion of shaft 9. The front end of the tool holder is mounted in casing 20 in a bearing 19 and has a flange 13a abutting bearing 19 in axial direction under the action of spring 17. However, when a screw driver 13b mounted in tool holder 13 is pressed against the screw, spring 17 is compressed, and tool holder 13 is displaced to the right as viewed in FIG. 2.

Coupling means are provided for connecting tool holder 13 with drive means 1, 2, 3. The coupling means include a coupling sleeve or member 24 which is mounted on a portion of tool holder 13 for rotation and axial movement. Coupling sleeve 24 carries at the ends thereof coupling parts 23 and 27 which respectively form with other coupling parts 21 on tool holder 13, and 4 on drive gear 3, an overload coupling 21, 23 and a drive coupling 27, 4.

The inner end portion of tool holder 13 is threaded, and has an axially extending groove 28a. An adjusting ring 25 is slidingly mounted on the threaded portion of tool holder 13, and secured against rotation by a pin 28 inserted into groove 2811. A threaded adjusting ring 26 is screwed onto the threaded portion and determines the axial position of adjusting ring 25. A diametrically extending groove of semi-circular cross section on the rear face of adjusting ring 25, and a corresponding rib on the front face of threaded adjusting ring 26 engage each other in the adjusted position of adjusting means 25, 26. The outer circular peripheral surface of adjusting ring 25 forms a bearing for the hollow end portion of coupling sleeve 24.

An overload spring 29 is located between coupling sleeve 24 and the inner portion of tool holder 13, and abuts with its ends a radial annular surface of coupling sleeve 24 and adjusting [ring 25. Consequently, overload spring 29 urges tool holder 13 to the right, and coupling sleeve 24 to the left as viewed in FIG. 1 so that the overload coupling 23, 21 is engaged. The drive coupling 27, 4 is disengaged in the normal position of the apparatus by effect of the spring 17 urging tool holder 13 and with it sleeve 24 to the left in FIG. 1.

The overload coupling 21, 23 includes a plurality of coupling rollers 21 mounted on flange 13a for turning movement about radial axes, and a plurality of coupling parts 23 at the end of coupling sleeve 24. Coupling parts 23 have slanted faces cooperating with rollers 21. In the normal position of the overload coupling 21, 23-, the overload coupling is engaged, and coupling sleeve 24 coupled with tool holder 13. However, if rotation of the tool and tool holder is blocked, for example if a screw has been fully driven into a material, the load torque becomes so high that the slanted faces of coupling parts 23 ride over rollers 21, and then snap again behind the same to assume again the engaged position. While the slanted faces of coupling parts 23 ride over rollers 21, coupling sleeve 24 is displaced to the right against the action of spring 29 which urges coupling sleeve 24 and coupling parts 23 to move to the left to the normal position in which coupling parts 21, 23 of the overload coupling are engaged.

The drive coupling includes a plurality of coupling fingers or teeth 27 on the end face of coupling sleeve 24, and a plurality of coupling fingers or teeth 4 on the confronting end face of drive gear 3.

In the normal inoperative position of the hand tool shown in FIG. 1, overload spring 29 urges overload coupling 21, 23 into the engaged position, spring 17 urges tool holder 13 forward until flange 13a abuts the axial face of bearing 19, while coupling sleeve 24 follows tool holder 13 to this position under the action of overload spring 29, and spring 6 holds drive gear 3 in a position abutting stop washer 10 so that the drive coupling 4, 27 is disengaged.

When the hand tool is used, the motor is started, and transmission 1, 2, 2a rotates drive gear 3 together with shaft 9. Tool holder 13 and coupling sleeve 24 are not yet rotated since coupling parts 4, 27 of the drive coupling are disengaged.

When the screw driver blade 13b is pressed against a screw thread by manual force acting on the rear end of casing 20', spring 17 is compressed since control member 16 is blocked by locking balls 15 which are confined in bores 14 by the inner surface of gear 3. Coupling sleeve 24 moves with tool holder 13 to the right until coupling parts 4, 27 of the drive coupling engage, and drive gear 3 rotates coupling sleeve 24 and by overload coupling 23, 21, also tool holder 13 so that the screw driver blade 13b turns the screw until the same cannot be turned any farther. In this position, rotation of tool holder 13 is blocked, and the rotated and driven coupling sleeve 24 turns coupling parts 23 relative to coupling rollers 21 so that the slanted faces of coupling parts 23 ride on rollers 21 and displace coupling sleeve 24 to the right.

During the driving of the screw, drive coupling 4, 27 was in the position of FIG. 2, and drive gear 3 was in its initial normal position. When coupling sleeve 24 is now displaced to the right, drive gear 3 is also axially displaced to the right against the action of spring 6 to a position shown in FIG. 3 in which its groove 5 registers with bores 14 so that locking balls 15 enter groove 5 and lock drive gear 3 in the axially displaced position shown in FIG. 3. Drive coupling 4, 27 remains at first engaged so that drive gear 3 rotates coupling sleeve 24 over the engaged drive coupling 4, 27 until coupling parts 23 have passed beyond the respective coupling rollers 21, and snap behind the same forwardly to the engaged position under the action of overload spring 29. This permits a movement of coupling sleeve 24 to the left under the action of overload spring 29, resulting in the separation of coupling parts 27 from coupling parts 4 on the locked drive gear 3, resulting in the position of FIG. 3. The tool holder assumes its normal position shown in FIG. 1 as soon as the screw driver blade is removed from the workpiece, and since drive coupling 4, 27 is disengaged, the tool holder is no longer rotated.

The return of tool holder 13 to the left to its normal position has relieved the pressure on spring 17 so that a lesser resilient force acts on control member 16. The force of spring 6 acts on drive gear 3 to push the same to the left out of the locked position of FIG. 3. A component of this resilient force acts through the slanted surface of annular groove 5 on locking balls 15 to urge the same inward into bores 14. The pressure of the balls acting on the conical face of control member 16 urges the same to the left, compressing spring 17, and after further movement of drive gear 3 by spring 6, he normal position of FIG. 1 is again assumed.

,-The spring forces and dimensions of springs 17 and 6 have to be selected so that spring 6 is only capable of releasing the locking means 15 when the pressure of spring 17 on control member 16 is reduced due to movement of the tool holder 13 to its normal position. In the position of tool holder 13 axially displaced to the right due to the manual pressure exerted on the hand tool, the tension of spring 17 is suflicient to prevent release of the locking means 15 from the locking position shown in FIG. 3.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of electric hand tools differing from the types described above.

While the invention has been illustrated and described as embodied in an electric screw driver having combined overload and drive coupling means, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A hand tool comprising, in combination, a casing; a tool holder and a drive means mounted in said casing for rotation and axial movement; coupling means connecting said tool holder with said drive means and including .an overload coupling, a drive coupling, and a rotary and axially movable coupling member connected with said couplings; an overload spring connecting said coupling member with said tool holder and urging said coupling member to a normal position in which said overload coupling is engaged; and a second spring for urging said tool holder and coupling member in said normal position to an inoperative position in which said drive coupling is disengaged, said tool holder, overload coupling, and coupling member from said normal position being moved by outer axial pressure to a working position in which said drive coupling is engaged and said tool holder is rotated by said drive means, while upon blocking of rotation of said tool holder, said overload coupling is momentarily disengaged and displaces said coupling member, said drive coupling, and said drive means in axial direction so that said drive means rotates said coupling member idly until said overload spring returns said coupling member to said normal position.

2. A hand tool according to claim 1 wherein said coupling member includes a coupling sleeve surrounding a portion of said tool holder; wherein said tool holder includes adjusting means mounted on said portions; and wherein said overload spring is located between said coupling sleeve and said portion, and has ends abutting said adjusting means and said coupling sleeve to urge the same and said tool holder to the normal position in which said overload coupling is engaged.

3. A hand tool according to claim 2 wherein said portion of said tool holder is threaded; wherein said adjusting means include a threaded ring adjustably mounted on said threaded portion for adjusting the tension of said overload spring.

4. A hand tool according to claim 2 wherein said overload coupling includes a first group of coupling parts on said tool holder and a second group of coupling parts on said coupling sleeve, at least said coupling parts of one of said groups having slanted faces for causing, upon blocking of said tool holder, axial movement of said coupling sleeve to a position in which said overload coupling is disengaged.

5. A hand tool according to claim 2 wherein said drive coupling includes coupling parts on said coupling member and coupling parts on said drive means.

6. A hand tool according to claim 1 wherein said overload coupling includes first and second coupling parts respectively secured to said tool holder and said coupling member; wherein said drive coupling includes third and fourth coupling parts respectively secured to said coupling member and to said drive means; wherein said first and second coupling parts are shaped to cause axial movement of said coupling member when said tool holder is blocked so that said coupling member displaces said drive means in axial direction beyond the engaged position of the drive coupling; and comprising locking means for holding said drive means in the displaced position while said second spring moves said tool holder with said coupling member and said third coupling parts to said normal position in which said drive coupling is disengaged; and releasing means for unlocking said locking means when said tool holder and coupling member are in said normal position.

7. A hand tool according to claim 6 including a third spring for holding said drive means in a normal position and being tensioned in said axially displaced position of said drive means; wherein said locking means are operated by said second spring; and wherein said releasing means is operated by said third spring overcoming said second spring in said normal position of said tool holder and said coupling member.

8. A hand tool according to claim 7 wherein said drive means includes a drive gear having said fourth coupling parts and being engaged by said third spring, said drive gear having a groove; wherein said locking means include a shaft having radial bores and supporting said drive gear for axial movement, locking balls mounted in said bores, and a control member having a slanted face engaging said locking balls and biassed by said second spring to urge said locking balls into locking engagement with said drive gear located in said groove of the same; and releasing means including a slanted surface of said groove of said drive gear engaged by said locking balls when locking said drive gear, and urging said locking balls to an inoperative position located in said bores when said drive gear is moved to its normal position by said third spring in said normal position of said tool holder in which said second spring exerts a lesser force on said control member than in said axially displaced position.

9. A hand tool according to claim 1 wherein said coupling member includes a coupling sleeve surrounding a portion of said tool holder; wherein said overload coupling includes cooperating coupling parts on said tool holder and on said coupling sleeve shaped to displace said coupling sleeve in axial direction when rotation of said tool holder is blocked; wherein said overload spring surrounds a portion of said tool holder and is surrounded by said coupling sleeve, said overload spring having ends abutting said tool holder and coupling sleeve to cause engagement of said overload coupling; wherein said drive means includes a shaft coaxial with said tool holder; a drive gear mounted on said shaft for rotation therewith and for axial movement between a normal position and an axially displaced position; including a third spring abutting said shaft and said drive gear and urging the same to said normal position thereof; wherein said drive coupling includes coupling parts on said drive gear and said coupling sleeve; and wherein by axial pressure on said tool holder said coupling sleeve is axially shifted so that said drive coupling is engaged, while upon blocking of said tool holder, said overload coupling further axially displaces said coupling sleeve so that said drive gear is moved to said axially displaced position; and including locking means for locking said drive gear in said axially displaced position until vanishing of said axial pressure on said tool holder permits said second spring to move said coupling sleeve and tool holder back to said normal position in which said overload coupling is engaged and said drive coupling is disengaged.

10. A hand tool according to claim 9 wherein said 7 tool holder portion and said stationary shaft have aligned axial recesses; including a control member for said locking means located in said axial recess of said shaft; and wherein said second spring is located in said recesses abutting said control member; and means for unlocking said locking means in said normal position of said tool holder and coupling sleeve when said overload coupling is engaged and said drive coupling is disengaged.

. 8 References Cited UNITED STATES PATENTS 11/1955 Amtsberg 8l-52.4 2,728,252 12/1955 Connell 81-52:.4 3,020,789 2/1962 Etzkorn 8l52.4 3,168,944

2/ 1965 Livermont 19256 BENJAMIN W. WYCHE, III, Primary Examiner. 

1. A HAND TOOL COMPRISNG IN COMBINATION, A CASING; A TOOL HOLDER AND A DRIVE MEANS MOUNTED IN SAID CASING FOR ROTATION AND AXIAL MOVEMENT; COUPLING MEANS CONNECTING SAID TOOL HOLDER WITH SAID DRIVE MEANS AND INCLUDING AN OVERLOAD COUPLING, A DRIVE COUPLING, AND A ROTARY AND AXIALLY MOVABLE COUPLING MEMBER CONNECTED WITH SAID COUPLINGS; AN OVERLOAD SPRING CONNECTING SAID COUPLING MEMBER WITH SAID TOOL HOLDER AND URGING SAID COUPLING MEMBER TO A NORMAL POSITION IN WHICH SAID OVERLOAD COUPLING IS ENGAGED; AND A SECOND SPRING FOR URGING SAID TOOL HOLDER AND COUPLING MEMBER IN SAID NORMAL POSITION TO AN INOPERATIVE POSITION IN WHICH SAID DRIVE COUPLING IS DISENGAGED, SAID TOOL HOLDER, OVERLOAD COUPLING, AND COUPLING MEMBER FROM SAID NORMAL POSITION BEING MOVED BY OUTER AXIAL PRESSURE TO A WORKING POSITION IN WHICH SAID DRIVE COUPLING IS ENGAGED AND SAID TOOL HOLDER IS ROTATED BY SAID DRIVE MEANS, WHILE UPON BLOCKING OF ROTATION OF SAID TOOL HOLDER, SAID OVERLOAD COUPLING IS MOMENTARILY DISENGAGED AND DISPLACES SAID COUPLING MEMBER, SAID DRIVE COUPLING, AND SAID DRIVE MEANS IN AXIAL DIRECTION SO THAT SAID DRIVE MEANS ROTATES SAID COUPLING MEMBER IDLY UNTIL SAID OVERLOAD SPRING RETURNS SAID COUPLING MEMBER TO SAID NORMAL POSITION. 